The use of biaxial films composed of a polymerizable cholesteric material has been proposed as a useful technology for improving the performance of liquid crystal displays (refer to PTL 1 and PTL 2). Biaxial films can be produced by applying a polymerizable cholesteric liquid crystal containing a dichromatic initiator to a substrate and then performing polymerization with polarized UV. However, there is a problem in that it is difficult to formulate a dichromatic initiator because both dichromatism and performance of a polymerization initiator need to be achieved, and thus only limited materials can be used. Furthermore, it is extremely difficult to impart, to a dichromatic initiator, the performance of a photoinitiator that can achieve curing in the air (in the presence of oxygen), and thus the atmosphere needs to be replaced with an inert gas such as nitrogen during irradiation with polarized UV. This poses problems such as an increase in production cost, an increase in takt time, and a decrease in process margin.
Biaxial films can be produced with a typical polymerization initiator used in the technical field of photo-radical polymerization, instead of a dichromatic initiator. By selecting a photoinitiator that can achieve curing in the air, curing can be performed with polarized UV without replacing the atmosphere with an inert gas. However, this poses a problem in that the performance as a biaxial film is not sufficiently provided. For example, regarding biaxial films used for liquid crystal displays, particularly VA liquid crystal displays, it is difficult to ensure that the front phase difference Re (defined as Re=(nx−ny)×d, where nx and ny represent refractive indices in a film in-plane direction, nz represents a refractive index in a thickness direction, and d represents a thickness) is 40 nm or more and the phase difference Rth in a thickness direction (defined as Rth=((nx+ny)/2−nz)×d, where nx and ny represent refractive indices in a film in-plane direction, nz represents a refractive index in a thickness direction, and d represents a thickness) is 180 nm or more.
To improve the front phase difference of biaxial films, a technology has been disclosed in which 5 to 60% of polymerizable liquid crystal compound having a carbon-carbon triple bond is added (refer to PTL 3). The front phase difference Re is only 8.5 nm when a compound having a carbon-carbon triple bond is not contained. In contrast, a front phase difference Re of 30 nm or more can be achieved with this technology. However, such a compound having a carbon-carbon triple bond has poor light resistance, which poses a problem in that a film formed by adding 5% or more of the compound easily turns yellow through exposure to light.